Solar ovens are cheap - and effective

Solar-box cookers focus the sun's rays and produce temperatures of between 100 and 150 degrees centigrade - enough to kill the majority of harmful bacteria.

The machines cost only £22 each - far less than incinerators or autoclaves.

Experts writing in the Lancet say that only 20 minutes of sunshine in an hour should be enough to make the simple devices work.

The problem of biomedical waste disposal is an expensive headache for clinics and hospitals throughout the developing world.

Incinerators and autoclaves are costly to build and buy, and some waste ends up being dumped without decontamination, increasing the risk of disease spread.

Simple design

Solar ovens are already used in countries such as India not only for cooking, and experts from the Department of Microbiology at Choithram Hospital and Research Centre in Indore decided to test their potential to "cook" biomedical waste.

The solar heating systems should provide a cheap disinfection option to treat infectious waste Researchers, Choithram Hospital, India

Solar ovens are extremely simple, consisting of two foil covered boxes, one fitting inside the other.

A sheet of transparent glass serves as a lid, and an angled mirror reflects extra sunlight into the box.

It works on the same principles as a greenhouse, reaching high temperatures quickly.

These are enough, say the researchers to pasteurise fluids placed within the box.

Field tests

Cotton wool contaminated with different bacterial samples such as Staphylcoccus and E.coli were placed in the box and kept in the oven for six hours during the day.

How much? Decontamination options Incinerator: £24,500 Microwave: £7,700 Autoclave: £41,000 Solar oven: £22

Bacteria levels were reduced to a fraction of those measured at the start of the experiment.

Other field trials using highly drug-resistant strains immersed in water were even more successful.

"The present units can be used in small clinics and health centres," the researchers wrote.

"Further, modification with parabolic or multiple mirror type solar cookers can provide much higher temperatures."

They wrote: "The solar heating systems should provide a cheap disinfection option to treat infectious waste in countries that are less economically developed."

Other doctors backed up this view.

Kevin McGuigan and Siobhan Kehoe from the Royal College of Surgeons in Ireland wrote, also in the Lancet, that the solar cookers would be of benefit to "many communities".